— 387 — 
It is therefore now recognized that Garigamopteris flora probably 
owed its origin to the existence, for atime, in Gondwna-land of a 
glacial climate which either exterminated or drove back and held 
in check for a considerable period the cosmopolitan flora, or so much 
of it as was not able, by mutation or adaptation, to withestand its 
rigor. 
Meanwhile the older Gondwana types, offshoots of the hardier 
elements in the Northern flora developed and distributed them- 
selves in both hemispheres. Though it is not supposed that they 
came into being under actual glacial conditions, there is hardly room 
for doubt that they appeared while the region was still cold and 
quite inhospitable to the contemporaneous northern, or cosmopoli- 
tan, types. 
The causes of the Palaezoic glaciation of Gondwana land are 
not yet agreed upon. Among the earlier hypotheses offered in 
explanation of the occurrence and area of the cold climate was a 
shifting of the earth’s axis so as to bring one of the poles in the 
region of the southern part of the Indian Ocean. Others are the 
great altitude of the surface of the land mass; a reduction of the 
carbonic acid gas (C O*) in the atmosphere through long periods of 
rock decomposition following uplifts the agencies of coal formation, 
the result being a loss of heat by radition and the establishment 
of climatic zones and the degree of salitiny and consequent care 
Oldham, Man. Geol. India, 2d Ed. , 1893, chaps. vi, and vii; Blanford, Quart. Journ. Geol. 
Soc. vol xlii, 1886, p. 249; Blanford, Rec Geol Surv, India, vol, XX, 1887, p. 49; Oldham, 
Geol. Mag., (3) vol. II!, 1887, p. 52. 
In Australia the glacial boulder beds are known to have been distributed over an area 
between longitude 137°,30’ E. and 151¢34’ E., and from 40°S. in Tasmania to the Bowen 
River coallield, 20°30’S. in Queensland. The criteria include boulders, rounded. facetted, 
and striated, in fine-grained silts; roches moutonnées, etc. Sevéral thousands of square 
miles im Victoria are said to be covcred with glacial conglomerates, which, with their 
included beds, attain a thickness of over 1000 meters, Nine or ten distinct boulder beds 
with thick intervening.deposits are observed in the Baccus Marsh series of this colony. 
The ice cap appears in some ragions to have moved in a general direction from south to 
north. See T, W. E. David, Quart. Journ. Geol. Soc. hi, 1896, p, 289; Penck, Zeitschr. 
Gesell, Erdkunde, vol. XXXV, 1900, no. 4, p. 239; David and Howchin, Trans. Roy. Soc: 
8. Australia, vol, XX, 1897, p, 61, and Rept. 7th Mecting Austr. Assoc. Adv, Sci., 1898, 
pg. 414; Officer and Hogg, Prog. Roy. Soc. Victoria, a. s., vol. X, 1897, pt. 1, p. 60, pt. 2, 
p. 180; R. M. Johnsten, Geol. Tasmania, 1888. 
In South Africa the Dwyka conglomerate reaches a thickness of over 350 meters, 
including boulder beds 20 meters in thickness, with facetted pebbles, etc. Kvidence of 
glacial culling, bossses, ctc., is seen at many points over an area including large portions 
of several of the colonies, See Geikie, Texl-book Geol. vol. II, 1903, p. 1057; Mohlengral, 
Bull, Soc. geol. Fr., (4) vol. 1.1901, pp. 18. 67, and Trans. geol. Soc. S. Afr., vol. IV, 
1838, p. 103, aud Trans. Phil. Soc, Afr., vol. XI, 1900, p. 113; Rogers, Trans S. Afr, 
Phild. Soc,, vol. XI, 1902; Anderson, 2d Ropt; Geol Surv. Natal and Zululand, 1904, pp. 
43,50; Girard, La Geographie, vol, ILI, 19U4, p. 423, and Bull. Soc, belg. geol. paleont,, 
Hydrol,, vol. XVI, 1902, p. 92; Davis, Bul. Geol. Soc. Amer., 1906 (not issued) and Dubois 
Archives Tyler, (2) vol. vii, pt. 4, 1901, and vol. viii, pt.4. 1902; The Geology of South. 
Alvica by P. H. Hotch add N.S. Corstorphine, 1905, 
